In modern papermaking, an ever-increasing emphasis is being placed on providing means which will increase productivity and minimize the content of solids in the wash water. These goals are normally provided by wet-end additives. Some of the benefits the papermaker realizes by increasing the drainage rate and the retention of particulate matter in the web being formed include better economic utilization of the furnish material, improved quality of the resultant sheet product, cleaner white-water effluent and, therefore, minimization of its treatment before release, and permitting of increase in rate and production by increased rate of drainage.
A large variety of materials have been used to provide increased drainage rate and as retention aids. The most widely used of these are salts of aluminum, in particular aluminum sulfate, sodium aluminate and sodium phosphoaluminate. These materials, however, have the defect of being required to be used in large amounts and do not exhibit high efficiency.
Various polymeric materials, from naturally occurring gums to synthetic resins, have been developed for use in papermaking. Included among the later catagory are polymers based on polyethyleneimine.
Polyethyleneimine is conventionally formed by ring opening of the monomeric compound, ethyleneimine. The resultant product is a water-soluble, high molecular weight, highly branched polymer having normally about 25 percent primary amine and 25 percent tertiary amine groups. The resultant polyethyleneimine, due to its water solubility and high amino nitrogen content, exhibits excellent properties with respect to drainage and retention when used in paper making processes. However, because the starting monomer, ethyleneimine, is a known carcinogen, the production and use of the resultant polymer has been drastically limited.
Other routes have been studied to form polyethyleneimine. One established route is by the use of an N-substituted oxazolines, such as the N-methyl derivative to produce a polymer having a linear configuration. When the polyacetylethylenimine intermediate is partially hydrolyzed, it yields a water-soluble, linear polymer having ethyleneimine units therein. These polymers, however, exhibit poor retention and drainage properties. When the polymer intermediate is more fully hydrolyzed the resultant linear polyethyleneimine is substantially insoluble in water and, therefore, cannot be used as a wet-end additive.
It is highly desired to be able to form a retention and drainage aid material based on a polyethyleneimine polymer which has a maximum amount of secondary amino groups therein, which is formed from non-carcinogenic material and which is capable of being added to and solvating in the aqueous slurry of the head-box of a paper forming process.